In recent years, a self-luminous display apparatus using a light-emitting element employing an electroluminescence (hereinafter referred to as “EL”) phenomenon has been developed as a display apparatus instead of a liquid crystal display apparatus.
The display apparatus including an EL element can emit light at a low voltage. As the display apparatus is self-luminous element, the display apparatus has a wide viewing angle and high viewability. In addition, use of a complete solid element having a thin-film shape allows the display apparatus to save space and thus to be portable, which makes the display apparatus more attractive.
The EL element has a configuration in which a light-emitting layer containing a luminescent material is provided between an anode electrode and a cathode electrode. The EL element emits light by the use of the light-releasing phenomenon observed when excitons generated by the recombination of the electrons and the holes having been injected into the light-emitting layer are deactivated.
The light-emitting layer in the EL element is formed mainly by the use of a vapor deposition technique such as the vacuum vapor deposition technique. The vapor deposition technique for forming a full-color organic EL display apparatus is roughly classified into a white color filter (CF) technique and a separate-patterning technique. In addition, a technique that is classified into neither the white CF technique nor the separate-patterning technique has been proposed in recent years. The technique combines the EL element with a color conversion layer.
In the white CF technique, the luminescent color of each subpixel is selected by combining an EL element emitting white light with a CF layer. According to the white CF technique, each subpixel emits white light by layering a red light-emitting layer, a green light-emitting layer, and a blue light-emitting layer between the cathode electrode and anode electrode. In addition, each subpixel includes color filters of red color (R), green color (G) and blue color (B), which allows such subpixels to compose a full-color display apparatus.
In the separate-patterning technique, a separately patterning vapor deposition is performed by the use of vapor deposition masks for individual colors. Commonly, subpixels including red color (R) EL elements, subpixels including green color (G) EL elements, and subpixels including blue color (B) EL elements are arranged on a substrate. The subpixels are selectively made to emit light of their respective colors with desired luminance by the use of TFTs to display intended images. Between every mutually-adjacent EL elements, a bank (partition) is disposed to define light emitting regions of the subpixels. The light-emitting layer in each EL element is formed in an opening in the bank by the use of a vapor deposition mask.
According to the technique combining the EL elements with color conversion layers, a blue light-emitting layer is formed as a common layer to all the subpixels. Each green subpixel includes a green color conversion layer configured to convert the blue light to the green light; and a green color filter. Each red subpixel includes a red color conversion layer configured to convert the blue light to the red light; and a red color filter. Each blue subpixel includes a blue color filter but does not include color conversion layer. Hence, the blue light emitted by the blue light-emitting layer is extracted through the blue color filter without having been subjected to any color conversion. Accordingly, each subpixel emits light of the corresponding color (e.g., see PTL 1).
The display apparatus disclosed in PTL 1 includes a pair of substrates that are arranged face to face each other. For each subpixel, a counter electrode layer is formed on a first one of the substrates, then a function layer including a blue light-emitting layer is formed on the counter electrode layer, and then an optical transparent electrode layer is formed on the function layer. On a second one of the substrates, a color filter and, if necessary, as described above, a color conversion layer are formed for each subpixel. The counter electrode layer is a layered body including a reflective electrode layer and a transparent electrode layer formed by layering these layers in this order from the first substrate side.
In the case of the display apparatus of PTL 1, the blue subpixels have no color conversion layers, and the optical distance between the reflective electrode layer and the blue light-emitting layer in each of the blue subpixels is set to a distance enabling the interference of the blue light in the blue light-emitting layer. Hence, the blue light that is extracted has an intensity increased by the interference. On the other hand, the red subpixels and the green subpixels include their respective color conversion layers. In each of the subpixels, the optical distance between the reflective electrode layer and the light-emitting layer is set to a distance enabling the light of the luminescent color obtained as a result of the conversion by the color conversion layer to be extracted with the highest intensity possible. Hence, the intensity of the extracted red light and the intensity of the extracted green light can be increased.